Impaired social interactions and motor learning skills in tuberous sclerosis complex model mice expressing a dominant/negative form of tuberin.

1Center for Neural Science, New York University, New York, NY 10003, USA.

Abstract

Tuberous sclerosis complex (TSC) is a genetic disorder characterized by the development of hamartomas in multiple organs. Neurological manifestation includes cortical dysplasia, epilepsy, and cognitive deficits such as mental impairment and autism. We measured the impact of TSC2-GAP mutations on cognitive processes and behavior in, ΔRG transgenic mice that express a dominant/negative TSC2 that binds to TSC1, but has mutations affecting its GAP domain and its rabaptin-5 binding motif, resulting in inactivation of the TSC1/2 complex. We performed a behavioral characterization of the ΔRG transgenic mice and found that they display mild, but significant impairments in social behavior and rotarod motor learning. These findings suggest that the ΔRG transgenic mice recapitulate some behavioral abnormalities observed in human TSC patients.

(A) y-water maze learning and memory, and reversal learning: both WT and ΔRG mice learned to choose the correct arm with the same efficacy. When tested (T) 24 hours later, both groups showed normal memory for the correct arm, followed by normal reversal learning of the original task (WT, n=13; ΔRG, n=17. p>0.05, two-way ANOVA). (B) Morris water maze: both WT and ΔRG mice learned to find the hidden platform with similar escape latency times during the initial six days of training. During reversal learning, both WT and ΔRG mice learned to find the new hidden platform location with similar escape latency times during the four days of reversal training. Both groups were able to find the escape platform with similar escape latency times during the two days of the visible version of the water maze. (WT, n=12; ΔRG, n=12. p>0.05, Two-way ANOVA). (C) probe trial quadrant occupancy: both WT and ΔRG mice spent significantly more time searching in the target quadrant compared to the other quadrants during the probe trial test (WT, n=12; ΔRG, n=12. p>0.05, [Quadrants, ***p<0.0001] two-way ANOVA). (D) probe trial platform crossings; both WT and ΔRG mice had a similar number of platform crossings in the target quadrant during the probe trial test (WT, n=12; ΔRG, n=12. p>0.05, two-way ANOVA). (E) probe trial latency: ΔRG mice spent significantly more time trying to find the platform zone than WT mice during the probe trial test (WT, n=12; ΔRG, n=12. *p<0.05, Student’s t-test).

(A) wild-type (WT) and ΔRG mice responded similarly during the acquisition of a contextual fear paradigm where two footshocks were presented one minute apart after a three minute period of habituation (WT, n=17; ΔRG, n=15. p>0.05, [training ***p<0.0001] Two-way ANOVA). (B) both WT and ΔRG mice had similar levels of freezing to the context 24 hours after training (WT, n=17; ΔRG, n=17. p>0.05, Student’s t-test) (C) both WT and ΔRG mice had similar levels of freezing to the context 7 days after training (WT, n=17; ΔRG, n=17. p>0.05, Student’s t-test).